Water Spangles (Salvinia minima) A Technical Review of Distribution, Ecology, Impacts, and Management May 2009 Alison Mikulyuk Michelle E. Nault Document citation: Mikulyuk, A. and M.E. Nault. 2009. Water Spangles (Salvinia minima): A Technical Review of Distribution, Ecology, Impacts, and Management. Wis‐ consin Department of Natural Resources Bureau of Science Services, PUB‐ SS‐1053 2009. Madison, Wisconsin, USA. Salvinia minima Front cover photo: J. LaForest, University of Georgia. Bugwood.org Back cover photo: T. Center, USDA‐Agricultural Research Service. Bugwood.org Inside image: University of Florida/Center for Aquatic & Invasive Plants. All images used with permission. The Wisconsin Department of Natural Resources provides equal opportunity in its employment, programs, services, and functions under an Affirmative Action Plan. If you have any questions, please write to Equal Opportunity Office, Department of Interior, Washington, D.C. 20240 This publication is available in alternative format (large print, Braille, audio tape, etc.) upon request. Please call (608) 266‐0531 for more information. Water Spangles, (Salvinia minima): A Technical Review of Distribution, Ecology, Impacts, and Management Alison Mikulyuk and Michelle E. Nault Bureau of Science Services This literature review was commissioned by the nonprofit Centre for Agricultural Bioscience International (CAB International; http://www.cabi.org/index.asp) as part of a larger invasive species compendium. We completed eight literature reviews for the project, and due to the large number of requests for this information, we have decided to make the reviews available as DNR miscellaneous publications. Species reviewed include: • Carolina fanwort (Cabomba caroliniana) – [PUB-SS-1047 2009] • European frog-bit (Hydrocharis morsus-ranae) – [PUB-SS-1048 2009] • Indian swampweed (Hygrophila polysperma) – [PUB-SS-1049 2009] • African elodea (Lagarosiphon major) – [PUB-SS-1050 2009] • Yellow floating heart (Nymphoides peltata) – [PUB-SS-1051 2009] • Curly leaf pondweed (Potamogeton crispus) – [PUB-SS-1052 2009] • Water spangles (Salvinia minima) – [PUB-SS-1053 2009] • Water chestnut (Trapa natans) – [PUB-SS-1054 2009] In completing the literature reviews, we preferentially consulted the peer-reviewed primary literature and supplemented the reviews with secondary sources where necessary. The outline for the reviews is identical for each species and was provided as part of the CAB International commissioning. This effort compliments work conducted during the development of the WDNR’s proposed invasive species identification, classification and control rule; a more exhaustive list of species and accompanying literature review summaries can be found on the DNR website at: http://dnr.wi.gov/invasives/ Identity Taxonomy and Nomenclature The heterosporous fern clade, of which Salvinia minima is a part, contains two families, Marsileaceae and Salviniaceae. These water ferns are the only group of heterosporous plants to have evolved heterospory after the Paleozoic. The group evolved and then diversified at the same time as flowering plants (Nagalingum et al., 2006). The family Salviniaceae is monogeneric, and includes ten species of Salvinia, all of which are highly morphologically similar (USDA-NRCS, 2008; Jacono et al., 2001). The names Salvinia auriculata Aublet and Salvinia natans (Linnaeus) Allioni and Salvinia rotundifolia Willdenow have been misapplied to Salvinia minima in several sources, and S. auriculata is occasionally erroneously listed as synonymous (Flora of North America Editorial Committee, eds., 1994+). Summary of Invasiveness Salvinia minima is a very productive free-floating, non-rooted aquatic fern native to South and Central America. Introduced to Southern Florida in 1926 (Jacono, 2003), the plant is degrading wetland ecosystems in several states (Tipping and Center, 2005). S. minima has an extremely high reproductive potential: the plants can rapidly colonize bodies of water, forming thick mats that displace native species, impact water quality, impede recreational activities, and clog waterways and irrigation channels (Rayachhetry et al., 2002). Salvinia is also resistant to desiccation, allowing it to be transported long distances out of water (ISSG, 2006). The species can act as an annual, dying back when temperatures decrease and causing harmful nutrient pulses and dissolved oxygen crashes (Dickinson and Miller, 1998). Distribution, Introduction, and Spread Distribution Salvinia minima occurs in lakes, riparian zones, water courses, wetlands and pools (ISSG, 2006) in warm temperate areas (Jacono et al., 2001). The species is common and wide-ranging from southern Mexico to northern Argentina and Brazil; however, the natural range in Argentina cannot be accurately determined due to the frequency of use in the water garden and aquarium trade (Jacono, 2003). The species is native to South America but is now established in the southern United States (Tipping and Center, 2005). These aquatic ferns have invaded drainage basins in Texas, Louisiana, Alabama, Arizona, California, Florida, Georgia, Hawaii, Mississippi, North Carolina and Oklahoma (Rayachhetry et al., 2002). The species grows best in slow-moving or still water and can tolerate salinity levels up to 7 ppt (ISSG, 2006). Risk of Introduction People commonly grow Salvinia spp. in aquaria and water gardens. Consequently, the plant has been distributed through related activities (Haynes and Jacono, 2000). Salvinia is still readily available in the aquaculture industry for direct purchase or can be included as a hitchhiker (ISSG, 2006). Since the species spreads not only clonally but also by spores, ship ballast water that contains spores can spread the plant internationally (ISSG, 2006). The earliest collection in North America was made around 1930 and was likely the result of ballast discharge of contaminated water in the St. Johns River near Jacksonville (ISSG, 2006). Plants were then documented in wide ranging locations across Florida and Georgia, which were likely the result of independent introductions (Jacono et al., 2001). Biology and Ecology Description S. minima is a deep green, free-floating, rootless, aquatic fern (ISSG, 2006). Stems can be up to 6 cm and leaves are from 1-1.5 cm long and almost round to elliptic. They are obtuse or notched at the apex and round to heart-shaped at the base. The upper surfaces of the fronds are covered with stiff hairs, with 4 separated branches. The under surfaces of the leaves are brown and pubescent with slender and unbranched hairs (Flora of North America Editorial Committee, 1993+). The stiff hairs on the fronds serve to trap air, thus providing buoyancy (Dickinson and Miller, 1998). Obscure veins are areolate and do not quite reach to the leaf edges. Sporocarps occur in groups of 4-8 with up to 25 megasporangia (Flora of North America Editorial Committee, 1993+). Similarities to Other Species All Salvinia species have stems with many multicellular hairs, leaves are horizontally spreading; floating leaves are green and pubescent. Sporocarps are borne on structures resembling cymes or on submerged leaves. Though the species resemble each other quite significantly, they can be distinguished from other floating leaf species by the unique upper side of the floating leaf (Flora of North America Editorial Committee, 1993+). Distinguishing among the various species in the Salvinia genus is difficult, and requires recognizing the differences in spore placement and leaf shape (Jacono, 2003). Habitat S. minima occurs in still or slow-moving water in tropical and warm temperate area of North and South America (Tipping and Center, 2005). It prefers the shallow backwaters in bayous, lakes and ponds, low-energy streams, oxbows, ditches, swamps and marshes (Jacono, 2003). It occurs frequently in waters with high organic content (UFL- IFAS, 2002), and typically inhabits water bodies with salinity levels as high as 4-7ppt (Jacono, 2003). Salvinia, due to its interesting morphology, is a popular aquarium and water gardening plant, it can grow fairly well in small, artificially constructed ponds (USACE-ERDC, 2002). Genetics The taxonomy of the genus Salvinia is relatively straightforward. The genus contains approximately 10 closely-related species in the monogeneric family Salviniacea. De la Sota and Cassa de Pazos (2001) report that the species S. minima has two distinct cytotypes: 2n=4x=36 and 2n=6x=54. The first population occurred in Brazil, and the second in Argentina. In its adventive range, genetic distances range to .48, which are high for an introduced, vegetatively reproducing plant (Madeira et al., 2003). Reproductive Biology S. minima reproduces vegetatively. Branching and fragmentation of rhizomes leads to the production of a high number of daughter plants (Jacono, 2003) The stiff hairs on the surface of the leaf helps to slow the desiccation of the plant, thus allowing it to spread long distances out of water (Jacono, 2003). Members of the genus occasionally reproduce via spores produced in sporocarps (USACE-ERDC, 2002), but fertile specimens are so rarely reported that the species is essentially considered sterile (Flora of North America Editorial Committee, 1993+). Physiology and Phenology High rates of vegetative reproduction occur throughout the growing season. Lateral buds are found deeply imbedded in the stem, and will also lie dormant during dry and cold periods, sprouting when warmer temperatures occur. Additionally, rhizome fragments can also lie